The invention generally relates to the human eye and, more particularly, the invention relates to the cornea of the human eye.
The cornea consists of three regions, the epithelial sheet, the stroma, and the endothelial lining. The epithelial sheet is the outermost region. It consists of between five to eight layers of cells and makes up approximately 10% of the thickness of the cornea. Moreover, the epithelial sheet is renewable, in other words, capable of re-growth. In addition, the epithelial sheet is filled with thousands of tiny nerve endings, making the cornea extremely sensitive to pain when the epithelial sheet is, for example, scratched. The stroma is the middle region. It is located behind the epithelial sheet and makes up approximately 90% of the thickness of the stroma. The endothelial lining is the innermost region. It is a single layer of cells located behind the stroma.
During refractive eye surgery, the shape of the stroma is changed. For example, in Photo Refractive Keratectomy (xe2x80x9cPRKxe2x80x9d) the shape of the stroma is changed with an excimer laser. First, however, the cells in the epithelial sheet are killed or removed using either a laser, a chemical, or a scraping device. After the PRK, the epithelial sheet grows back over the stroma. However, during this time period, the patient may experience pain and/or poor vision. In addition, regression might occur. Regression is the growth of the epithelial sheet in a pattern which restores, or nearly restores, the shape of the cornea prior to the PRK.
In Laser Assisted In Situ Keratomileusis (xe2x80x9cLASIKxe2x80x9d), the shape of the stroma is also changed using an excimer laser. In LASIK, a microkeratome is used to hinge back the outermost 20-30% of the cornea. The excimer laser is then used to change the shape of the exposed stroma. Because LASIK maintains the epithelial sheet, LASIK tends to avoid the problems discussed above in regard to PRK. However, LASIK is dependent on the use of the microkeratome, which may jam, shred, or lose the corneal xe2x80x9cflap.xe2x80x9d Moreover, a suction device must be used in conjunction with the microkeratome, increasing intra ocular pressure up to approximately 100 mm Hg. For some vulnerable patients, the increase in intra ocular pressure can harm their eyes.
In Laser Epithelial Keratomileusis (xe2x80x9cLASEKxe2x80x9d), the epithelial sheet is loosened with an alcohol solution, then rolled back to expose the stroma. The excimer laser is then used to change the shape of the stroma and the loosened epithelial sheet is repositioned over the stroma. However, in LASEK, the patient experiences a slow return to clear vision and must wear a contact lens on the affected eye for a number of days. The slow return to clear vision is due to the use of the alcohol solution, which kills some of the epithelial cells. Moreover, the presence of dead epithelial cells renders the cornea vulnerable to infection, a situation that is enhanced because of the post-operative use of a contact lens.
In accordance with one embodiment of the invention, a method of delaminating the epithelial sheet of the cornea of a human eye comprises loosening the epithelial sheet with a loosening solution, the loosening solution including an agent, and separating the loosened epithelial sheet from the underlying tissue of the cornea. The agent may be hyaluronidase ACS. In particular, the agent may be a dose of hyaluronidase ACS between 30 International Units and 1000 International Units. In addition, the agent may be chondroitinase AC, chondroitinase ABC, keratanase, hyaluronidase, matrix metalloproteinase-1, matrix metalloproteinase-2, or matrix metalloproteinase-3. Further, the agent may be an activator of an endogenous enzyme that acts on the structure of the epithelial sheet.
In one embodiment of the invention, the process of loosening the epithelial sheet may include applying the loosening solution to the epithelial sheet of the cornea. For example, the loosening solution may be applied to the epithelial sheet using an eye well, in which the eye well is placed on the epithelial layer of the cornea and then the eye well is filled with the loosening solution. In an alternative embodiment of the invention, the loosening solution may be applied to the epithelial sheet using an absorbent material, in which the absorbent material is saturated with the loosening solution and then the absorbent material is placed on the epithelial sheet of the cornea. In a particular embodiment of the invention, the absorbent material may be a soft contact lens. After applying the loosening solution to the epithelial sheet of the cornea, the eye may be irrigated.
In these embodiments of the invention, when the loosening solution includes a dose of hyaluronidase ACS equal to 300 International Units, then the process of irrigating may occur substantially 90 seconds after the process of applying the loosening solution. In the alternative, when the loosening solution includes a dose of hyaluronidase ACS equal to 50 International Units, then the process of irrigating may occur substantially 120 seconds after the process of applying the loosening solution.
In an alternate embodiment of the invention, the process of loosening the epithelial sheet may include injecting the loosening solution into the top layer of the stroma. In the alternative, the process of loosening the epithelial sheet may include injecting the loosening solution into the middle layer of the stroma. In these embodiments of the invention, the loosening solution may include a dose of hyaluronidase ACS between 30 International Units and 50 International Units. In addition, the process of separating the loosened epithelial sheet may occur less than 180 seconds after the process of injecting the loosening solution.
In all of these embodiments of the invention, the process of separating the loosened epithelial sheet may include separating a portion of the loosened epithelial sheet. In addition, the process of separating the loosened epithelial sheet may include a traumatic separation. Atraumatic separation may include the use of a blunt edge, which may be attached to a vibrating system, or the use of a jet spray. The jet spray may be a jet of saline, water, or viscoelastic material. The process of separating the loosened epithelial sheet may further include the use of a physiological lubricant.
Further, the separated epithelial sheet may be placed back on the underlying tissue of the cornea. When replaced, a blood-clotting element may be applied to the epithelial sheet of the cornea to facilitate healing. In a particular embodiment of the invention, the blood-clotting element may be fibronectin. Moreover, the cornea may be anesthetized prior to the process of loosening the epithelial sheet.
In accordance with another embodiment of the invention, a method of delaminating the epithelial sheet from the cornea of a human eye comprises making an incision in the epithelial sheet, loosening the incised epithelial sheet using a loosening solution, the loosening solution including an agent, and separating the loosened epithelial sheet from the underlying tissue. In one embodiment of the invention, the incision is a circular incision, dividing the epithelial sheet into a first section inside the circular incision and a second section outside the circular incision. In this embodiment, the process of separating the loosened epithelial sheet includes dissecting the first section of the loosened epithelial sheet. In an alternate embodiment of the invention, the incision is a cruciate incision, dividing the epithelial sheet into four sections. In this alternate embodiment, the process of separating the loosened epithelial sheet includes rolling back the four sections of the loosened epithelial sheet. The process of separating the loosened epithelial sheet may also include separating at least a thin layer of the top layer of the stroma.
In accordance with a further embodiment of the invention, a method of administering a medicine through the epithelial sheet of the cornea of a human eye comprises applying a treatment solution of the medicine to the eye, the treatment solution including an agent. The agent may be hyaluronidase ACS. In particular, the agent may be a dose of hyaluronidase ACS between 30 International Units and 50 International Units. In addition, the treatment solution may include insulin. In the alternative, the treatment solution may include an antibiotic. In these embodiments, the process of applying a treatment solution may include the use of eye drops.